How to prune trees
There are two main reasons to prune a tree: To enhance its health and vigor or to make it grow the way you want. Some specific
benefits of both approaches:
Reduce crowding. Trees such as crabapple develop dense crowns over time. Removing some of the twiggy growth crowding the tree's interior allows
more sunlight to enter and air to circulate, reducing the chance of disease and pests. The new growth after pruning is also
more disease-resistant. Many trees sometimes produce two branches that grow in the same direction and compete for the same
space. In that case, you'll want to remove the less esthetic or robust branch to provide room for the other to flourish.
Repair or prevent damage and ensure safety. Broken, ragged branches are vulnerable to various insects and diseases. Branches that are dying, dead, or diseased should
also be removed as soon as possible to prevent the disease from spreading and the branch from falling on its own. Trees growing
over your house or other structures should be inspected annually for signs of decay so that threatening limbs can be removed.
Manage wayward growth. Any tree can occasionally produce branches that brush against the house, hang too low over a pathway, or block the view from
a window.
Increase or improve flowers or fruit. Proper pruning can dramatically increase the quality and quantity of flowers or fruits a tree produces. Pruning a crape myrtle
(Lagerstroemia) in later winter will produce more flowers in summer, for example.
When to prune
Light pruning--removing dead or broken branches--is safely done any time of year. But some times are better than others for
different needs.
To invigorate a tree. Late-winter or early spring pruning is best for most trees, since it allows the tree to concentrate its stored energy on
fewer branches. This leafless time also eases pruning by reducing cleanup and letting you see the tree's shape. Regrowth covers
the pruning shortly, and pruning wounds quickly begins healing. Late winter and early spring are also when to prune trees
that flower in summer, such as crape myrtle (Lagerstroemia), to encourage vigorous growth that produces summer flowers.
To retard growth. Late-spring or early summer pruning is best for slowing the growth of fast-growing trees. Summer pruning also tends to reduce
the number of suckers that sometimes grow around pruning cuts. Prune trees that tend to ooze or bleed after pruning during
the warm temperatures of summer. These include birches (Betula), dogwood (Cornus), maples (Acer), and walnuts (Juglans).
Hint: In hot-summer areas, avoid removing too much foliage from trees with thin bark,
which can become sunburned.
How to prune
Pruning is easy and requires nothing more than a pair of pruning shears to get started. But pruning to solve or prevent problems,
to make a tree attractive or productive, or to minimize future work takes a bit of understanding and thought.
Thinning. This is how to prune most trees. The word invites confusion because it refers to both a pruning cut and a desired result.
A thinning-type pruning cut means to remove a branch either at its origin or to an adjoining branch. Doing so encourages subsequent
growth to follow the tree's natural branching pattern. Thinning also means selectively removing branches to allow light and
wind to penetrate the tree.
| Thinning large limbs |
Thinning small limbs |
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| Thinning a tree means cutting at or near another branch. It encourages remaining branches to grow and retains the tree's natural
shape. |
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Heading or topping. This method of pruning is rarely desirable. Cutting to shorten a branch or stem at an essentially random point is a heading
cut. Heading cuts stimulate growth to occur just below the cut, usually clustered together. Heading large branches of mature
trees produces vigorous, twiggy growth that ruins the natural shape.
Hedge-shearing refers to multiple heading cuts on small branches. A hedge's thin exterior layer of leaves and leafless, twiggy
interior is typical of the growth produced.
Heading a tree means cutting a branch at an essentially random place. Subsequent growth is clustered near the cut.
Removing heavy branches. Ripped bark caused by pruning off a heavy branch is a common cause of long-term damage. Prevent this by removing most of
the weight from the branch first, several inches out from the final cut. Called a three-saw cut, this is the only way to safely
remove any branch that may tear bark.
1. Cut up from the bottom about a foot farther out from the location of the final cut. Cut about a third of the way through
the branch or until the saw begins to bind.
2. Cut down from the top an inch or two farther out on the branch. Once you've cut about half way through the branch, its weight
will force it to break at the point of the bottom cut, and the branch will fall off.
3. Remove the remaining stub. Don't cut flush with the main trunk; that would create an unnecessarily large wound. Cut from
the top or bottom just beyond the place where the branch and trunk join, called the branch collar, which is often indicated
with prominent ridges of bark.
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Getting professional help
Think twice before attempting the following:
Pruning high in a tree without safety ropes. Most homeowners are better off working from the ground, with a ladder and pole pruner.
Using a chain saw. This is especially risky in trees, on a ladder, and whenever you're working with it above chest height.
Call a pro for these kinds of cuts:
Branches that can fall onto a structure or into the street. Wood density varies, but as a guide, assume that a cubic foot of wood weighs about 50 pounds. Any subordinate branches and
leaves add to the weight.
Where there are utility wires. Aluminum pruning poles and ladders conduct electricity--a potentially lethal situation if they touch a live wire. Check with
the utility that owns the wires; they may prefer to manage the pruning themselves and handle the costs. Or, they may prefer
to interrupt service and drop the wire until pruning is completed. If you damage the wire, you could be charged for the repair.
For more information about tree pruning, check with these organizations:
• The International Society of Arboriculture (www.isa-arbor.com)
• The American Society of Consulting Arborists (www.asca-consultants.org)
• National Arborist Association (www.natlarb.com)
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